The present invention is directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, the invention provides a method of manufacturing a semiconductor integrated circuit device including a high surface area capacitor with a low depletion ratio. Merely as an example, an embodiment provides a method for a semiconductor integrated circuit device including a rapid thermal process after phosphorous doping of a hemispherical grained poly-silicon film.
Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as each process used in IC fabrication has a limit. That is to say, a given process typically only works down to a certain feature size, and then either the process or the device layout (“design rules”) needs to be changed. An example of such a limit is the amount of charge stored within a capacitor formed on the surface of a semiconductor device, given the low operating voltage of the semiconductor integrated circuit device due to its small geometry. The surface area of the storage determines the amount of charge that can be stored on the capacitor.
The manufacturing of integrated circuits involves various processes. For example, the processes include, inter alia, wafer growth, photolithography, doping, oxidation, deposition, etc.
Semiconductor devices and circuits are formed in wafers, which serve as substrates. Generally, single-crystal substrates, which are made from a single material with crystals formed by atoms all aligned in a specific direction. The process of waver creation usually involves creating a large ingot of semiconductor materials, aligning the ingot, removing impurities, slicing ingot into thin wafers, and polishing the sliced wafers.
Generally, photolithography process is used to define and shape specific areas of the wafer to suit particular design of integrated circuit. Usually, a layout design is used to create an optical mask (or reticle pattern, depending on application). The wafer surface is usually covered with a layer of photoresist. The wafer is then exposed to light through the optical mask. After light exposure, the areas of photoresist that were exposed to light are removed using chemical process. As a result, the wafer contains both clear areas (where photoresist is removed) and areas blocked by photoresist. Next, various processes (such as etching, oxidation, diffusion, etc.) only affecting clear areas are performed. After various process are finished, photoresist materials are then removed.
One of the various processes is oxidation, which is used to create insulating layers. Often, oxide grows on silicon in a wafer to form dielectrics made of SiO2. One of the method to grow oxide on wafer is exposing wafer to O2 at high temperatures.
Deposition is another process in semiconductor fabrication. Deposition provides connections among insulators and interconnecting layers by depositing various materials. Techniques such as chemical vapor deposition (CVD) and low pressure CVD (LPCVD) are commonly used. For example, metals are deposited to provide low resistance interconnects, polysilicon is used as conductor, and dielectric materials are deposited to create insulating layers.
Another process is doping, which changes the electrical properties of the wafer. For example, a specific area of the wafer may be doped and become n-type or p-type depending upon the doping material and concentration. There are a few ways to perform doping. One way is implantation, in which atoms are injected into wafers at high velocity. Another way of doping is through diffusion, in which atoms are diffused into selected regions of the wafer at high temperature.
For semiconductor memories of the dynamic random access types, i.e., “DRAMs,” information is stored by varying the amount of charge within each capacitor of an array of capacitors formed on the surface of a semiconductor substrate. For example, a bit (binary information) is stored at each capacitor by associating a discharged capacitor state with a logical zero and a charged capacitor state with a logical one. Reducing the size of a DRAM capacitor with reduced design rules reduces the surface area of the capacitor plates and therefore has the effect of reducing the amount of charge stored on the capacitor. In addition, the reduced surface area can degrade capacitor storage performance at low voltages.
A capacitor generally consists of two conducting plates placed in parallel separated by an insulator. The plates can be formed by two electrodes having a planar, cylindrical, or deep-trench surfaces. Applying a voltage differential to the electrodes charges the capacitor, where the surface of the electrodes will take on equal and opposite charges. The capacitor is fully charged when the voltage difference between the two electrodes is equal to the power supply voltage. If the capacitor is perfect, it will hold the stored voltage for an infinite time. Due to the leakage current inherent in a capacitor, the capacitor must be periodically recharged (refreshed) in order to keep the stored binary information. Therefore, the frequency of recharging (i.e., refresh rate) depends on the amount of stored charge and the amount of leakage current in the capacitor.
Conventional capacitor structures have been widely used in integrated circuit applications, such as DRAM. However, these capacitor structures have various limitations, some of which are described in more detail below.
Therefore, it is desirable to have improved methods of forming a semiconductor capacitor in the manufacturing of integrated circuits.